The invention relates generally to improved piston rings for use in internal combustion engines. It relates especially to a chrome insert ring for use as a pressure ring, which has annular chrome plate bands in the outer peripheral surfaces of the ring matrix.
Conventionally, various kinds of constructions in piston rings, especially pressure rings, have been proposed in recent years for adaptation to high speed and high power internal combustion engines. It is well known in the art that a chrome insert ring, which has annular hard chrome plate bands in grooves in the outer peripheral surface of the ring and a cast iron matrix exposed between the chrome plate bands, exhibits desirable performance as a pressure piston ring. In such chrome insert ring, the hard chrome plate bands serve to improve the abrasive resistance of the ring, and the exposed cast iron matrix serves to reduce the initial period for mating the ring to the engine and to compensate for the poor oil maintaining property of the chrome plate bands.
However, there have been certain disadvantages connected with the production process for conventional chrome insert rings. That is, as shown in FIG. 1, the insert ring is produced by stacking and fixing a plurality of ring elements CP1, CP2, . . . , each of which is formed with an annular groove 21 or 22 of trapezoidal cross section in the center portion of the outer peripheral surface thereof, and removing the portion of chrome not in the groove by cutting the structure along the chain line A, so as to expose the cast iron matrix between the chrome plate bands and at the top and bottom of the piston ring face.
During the plating operation, the projections at the opposite sides of the groove 21 prevent smooth plating to the groove bottom, especially to the groove corners in the vicinity of the opposite sides, so that the resulting chrome plate has its surface formed with annular recesses 4. This requires a long plating time, which is substantially three times that required for the case of a chrome plate produced with no recess all over the chrome plate surface, and has a strong influence on cost.